Asymmetric Bipolar Pulsed dc Sputtered Niobium Nitride Films for Electrode Materials in Supercapacitors.

Niobium nitride (NbN) films were deposited using asymmetric-bipolar pulsed dc sputtering at different pulse parameters. Microstructural, electrical and mechanical characterizations were performed by FE-SEM, AFM, LCR meter and nanoindentator. The results show that pulse frequency has significant effects on coating's microstructure, structural and electrical properties of NbN films. With an increase in pulse frequency, coating microstructure evolved from a porous columnar structure to a highly dense one. Average crystal grain sizes of NbN films were decreased from 52.7 nm to 27.5 nm with an increase in pulse frequency. The minimum resistivity of 351 μΩ-cm, the smoothest surface morphology with Ra roughness of 0.4 nm and the maximum hardness of 17.4 GPa were obtained for the films deposited at pulse frequency of 50 kHz, respectively.